John Calvin Commentary Romans 3:13

"Their throat is an open sepulchre; With their tongues they have used deceit: The poison of asps is under their lips:" — Romans 3:13 (ASV)

It is further added, Their throat is an open grave; that is, a gulf to swallow up men. It is more than if he had said that they were devourers (ἀνθρωποφάγους — men-eaters); for it is an intimation of extreme barbarity, when the throat is said to be so great a gulf that it is sufficient to swallow down and devour men whole and entire. Their tongues are deceitful, and the poison of asps is under their lips, mean the same thing.